Psychometric Validation Of The North Star Assessment For Limb-Girdle Type Muscular Dystrophies (NSAD) In Limb-Girdle Muscular Dystrophy Sarcoglycanopathies (LGMD 2C/2D/2E) Using Baseline JOURNEY Data...
Author(s)
Intan Purnajo, MPH1, Piper Fromy, PhD2, Linda Lowes, PhD1, Meredith K. James, PhD3, Ivana Filipovic Audhya, BSc, MSc1.
1Sarepta Therapeutics, Inc., Cambridge, MA, USA, 2SeeingTheta, Saumur, France, 3The John Walton Muscular Dystrophy Research Centre, Newcastle Upon Tyne, United Kingdom.
1Sarepta Therapeutics, Inc., Cambridge, MA, USA, 2SeeingTheta, Saumur, France, 3The John Walton Muscular Dystrophy Research Centre, Newcastle Upon Tyne, United Kingdom.
OBJECTIVES: Limb-girdle muscular dystrophies (LGMDs) are a group of rare, clinically and genetically diverse neuromuscular diseases. The North Star Assessment for limb-girdle type muscular dystrophies (NSAD) is a 29-item clinician-reported outcome measure that assesses muscle function. Although NSAD was evaluated in a previous Rasch analysis, additional psychometric properties need to be investigated among LGMD sarcoglycanopathies. This analysis explores the psychometric properties of NSAD in specific LGMD sarcoglycanopathies (LGMD2C/R5, 2D/R3, 2E/R4) using baseline data from patients in the JOURNEY natural history study (NCT04475926).
METHODS: Item-level performance of NSAD was evaluated by analyzing the item response distribution, inter-item correlations, and item-total correlations. Scale-level performance was evaluated by analyzing internal consistency, test-retest reliability, convergent validity, and known-groups validity.
RESULTS: A total of 138 patients was assessed. Although all response options for each NSAD item were endorsed, more than 33% of patients scored each item at the lowest response level (ie, ‘unable to do’). Inter-item and item-total correlations were all high, with most r values >0.7. The NSAD demonstrated excellent internal consistency (Cronbach’s alpha = 0.986) and test-retest reliability (ICCs >0.9). Convergent validity was demonstrated as all observed associations between NSAD and convergent clinical or patient-reported outcome measures met or exceeded the expected hypothetical relationships. Regarding known-groups validity, NSAD demonstrated monotonic trends by ambulatory status and by Global Assessment of Severity, Hand and Arm Ability, with large effect sizes [≥0.8] observed when comparing various adjacent groups.
CONCLUSIONS: While the results were not presented for ambulatory and non-ambulatory patients separately, the clinical impact of ambulatory status may be of significance. NSAD demonstrates good psychometric properties, evidenced by robust item-level performance, internal consistency, test-retest reliability, convergent validity, and known-groups validity, confirming the suitability of NSAD for assessing disease progression in patients with selected LGMD sarcoglycanopathies.
METHODS: Item-level performance of NSAD was evaluated by analyzing the item response distribution, inter-item correlations, and item-total correlations. Scale-level performance was evaluated by analyzing internal consistency, test-retest reliability, convergent validity, and known-groups validity.
RESULTS: A total of 138 patients was assessed. Although all response options for each NSAD item were endorsed, more than 33% of patients scored each item at the lowest response level (ie, ‘unable to do’). Inter-item and item-total correlations were all high, with most r values >0.7. The NSAD demonstrated excellent internal consistency (Cronbach’s alpha = 0.986) and test-retest reliability (ICCs >0.9). Convergent validity was demonstrated as all observed associations between NSAD and convergent clinical or patient-reported outcome measures met or exceeded the expected hypothetical relationships. Regarding known-groups validity, NSAD demonstrated monotonic trends by ambulatory status and by Global Assessment of Severity, Hand and Arm Ability, with large effect sizes [≥0.8] observed when comparing various adjacent groups.
CONCLUSIONS: While the results were not presented for ambulatory and non-ambulatory patients separately, the clinical impact of ambulatory status may be of significance. NSAD demonstrates good psychometric properties, evidenced by robust item-level performance, internal consistency, test-retest reliability, convergent validity, and known-groups validity, confirming the suitability of NSAD for assessing disease progression in patients with selected LGMD sarcoglycanopathies.
Conference/Value in Health Info
2025-11, ISPOR Europe 2025, Glasgow, Scotland
Value in Health, Volume 28, Issue S2
Code
PCR198
Topic
Clinical Outcomes, Health Technology Assessment, Patient-Centered Research
Topic Subcategory
Instrument Development, Validation, & Translation
Disease
Musculoskeletal Disorders (Arthritis, Bone Disorders, Osteoporosis, Other Musculoskeletal), Rare & Orphan Diseases